The modulation of 5-HT2C receptor (5-HT2CR) function holds a tremendous amount of therapeutic promise for the treatment of diseases of significant unmet medical need, including addiction, anxiety, depression, obesity/eating disorders and schizophrenia. Successful development of 5-HT2CR ligands requires selectivity versus the highly homologous 5-HT2AR and 5-HT2BR, because agonism at these receptors can result in serious CNS and cardiovascular adverse events. The rationale for this proposal is that allosteric modulators of the 5-HT2CR present a unique drug design strategy to augment the response to endogenous 5-HT in a site- and event-specific manner. This novel approach of using allosteric modulators of the 5-HT2CR to develop novel probes and therapeutics is very attractive since it is much easier to achieve high receptor subtype selectivity or even absolute specificity with a ligand binding to the allosteric site than with orthosteric ligands that bind to the endogenous ligand binding site. To date only one compound, PNU-69176E, has been identified via the compound library screening as a 5-HT2CR allosteric modulator. However, the relevant structure-activity relationship (SAR) studies were sparse, and thus our knowledge in this regard is quite limited. Our objective in this application is to optimize and develop allosteric modulators of the 5-HT2CR to generate novel, highly selective and potent 5-HT2CR ligands that will act as small molecule probes for the nervous system and novel therapeutics for CNS disorders. To accomplish this objective, we plan to pursue the following two specific aims: 1) Chemical synthesis and optimization of small molecules based on PNU-69176E as the chemical lead; and 2) Biological characterization of newly synthesized compounds using a cell-based signaling assay to identify allosteric modulators of 5-HT2CR with high potency, selectivity and better drug-like properties. This project is innovative, potentially high impact research that will aid in elucidating information about the chemical neurobiology of allosteric modulation of 5-HT2CR. Our results are expected to provide the valuable SAR and novel mechanistic insight into these chemically unique allosteric modulators of 5-HT2CR.The proposed studies will identify small molecules that will be utilized to probe the neurobiology of the 5-HT2CR. The long term goal of this project is to develop these modulators for preclinical validation and clinical application in translational research and ultimately as novel therapeutic candidates.